Justin Bieber parties with a boatload of models -- literally! Because what else are the young to do?

A source tells ET that the 21-year-old appearance-maker spent the weekend with about 10 women -- mostly models based in Los Angeles -- hanging out on a boat docked in Orange County, California. The source also says that Justin knew most of the ladies prior to the rendezvous.

The singer posted a photo from the event on Instagram, writing, "Good times good people good luck."